1. Field of the Invention
The present invention relates to a method for activating an alkaline storage cell which comprises a non-sintered type nickel positive electrode so as to improve the utilization of active material comprised of metallic cobalt powder.
2. Description of the Related Art
Recently, a non-sintered type nickel positive electrode comprising a core material to which a pasty active material is loaded has been widely used. Compared to the conventional sintered type nickel positive electrode, the non-sintered type nickel positive electrode has the advantages of simple production process, low production costs and attainment of high energy density.
In the non-sintered type nickel positive electrode, a high porous nickel substrate possessing the porosity of higher than 95% such as a sponge type nickel or a felt type nickel is employed as the electrically conductive core material. Further, an electrically conductive powder such as a cobalt compound powder is fixed in the active material so that electrical conductivity among the active material particles away from the nickel substrate increases. Consequently, the utilization of the active material improves. Particularly, as disclosed in Japanese Laid-open Patent Application No. 53-51449, metallic cobalt is known to improve the utilization owing to its electrically conductive characteristics. Also, at charging, the metallic cobalt is converted into the cobalt oxyhydroxide according to Formulae 2 and hereinafter 3, which is superior in electrical conductivity, and hence conductivity among the active material particles further increases.
Actually, owing to the metallic cobalt fixed in the cathode, the utilization of the nickel active material improves; and the cell capacity will improve. The improvement of the cell capacity, however, will not be sufficient only by fixing the metallic cobalt in the cathode. According to the alkaline storage cell disclosed in Japanese Laid-open Patent Application No. 64-21864, for example, the current at the initial state of the charging is suppressed so that oxidation of the metallic cobalt is given the highest priority.
This method, however, still fails to obtain the oxidation of the metallic cobalt which is smooth enough to improve utilization of the metallic cobalt; and hence the energy density of the cell has not improved as much as expected.